1. Field of the Invention
The present invention relates to a voltage conversion apparatus, a power output apparatus, and a control method of a voltage converter. Particularly, the present invention relates to control of a voltage converter that converts voltage between a driving device that drives an electric motor in a power running mode or regeneration mode and a DC (Direct Current) power source.
2. Description of the Background Art
Recently, attention is focused on hybrid vehicles and electric vehicles as vehicles taking into account environmental issues.
A hybrid vehicle includes, in addition to a conventional engine, a DC power source, an inverter, and a motor driven by the inverter as the power source. In addition to achieving the power by driving the engine, the voltage from the DC power source is converted into AC (Alternating Current) voltage by the inverter, and the converted AC voltage is used to drive the motor to achieve power. An electric vehicle includes a DC power source, an inverter, and a motor driven by the inverter as the power source.
Some of the hybrid vehicles and electric vehicles employ the approach of boosting the voltage from the DC power source by a boost converter and providing the same to the inverter. Japanese Patent Laying-Open No. 2004-229399 discloses a voltage conversion apparatus including such a boost converter. This voltage conversion apparatus supplies power to the inverter that drives the AC motor such that excessive current does not flow to the circuit element that conducts the boosting operation even if the voltage command value of the boost converter increases drastically.
However, the publication of Japanese Patent Laying-Open No. 2004-229399 is silent about a problem of the inverter voltage (the voltage between the boost converter and inverter) attaining an overvoltage level when the power balance of the AC motor is continuously at the regeneration side.
Even if the power balance of the AC motor temporarily attains the regeneration side, the inverter voltage will not become excessive since the regeneration power is absorbed by the capacitor arranged between the boost converter and the inverter. However, when the power balance of the AC motor is continuously at the regeneration side when the inverter voltage is controlled at the vicinity of the upper limit value by the boost converter, control of the boost converter cannot follow the rise of the inverter voltage, leading to the possibility of excessive inverter voltage.